A low-cost and high-strength soluble magnesium alloy and its preparation method

Abstract

The present invention discloses a low-cost high-strength soluble magnesium alloy and a preparation method thereof, belonging to the technical field of magnesium alloys, and solves the problems of low strength and poor solubility of magnesium alloys used as temporary plugging tools in the prior art. The components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7% - 9%, Ca: 0 - 1%, In: 0 - 0.5%, Cu: 0.1% - 1%, Ni: 0.1% - 1%, X: 0 - 1%, where X is one or more of FeCl3, C, and Zr, and the balance is Mg and inevitable impurities. The low-cost high-strength soluble magnesium alloy of the present invention has relatively high strength and relatively high dissolution rate.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy materials, and particularly relates to a low-cost and high-strength soluble magnesium alloy and a preparation method thereof. Background Art

[0002] Shale gas is a cleaner and more environmentally friendly unconventional natural gas, and has gradually become the main growth point of China's natural gas production. The shale gas horizontal well staged fracturing technology is the key technology for the efficient development of shale gas. Its main principle is to inject fluid under a pressure higher than the target formation pressure, so as to form more fractures in the production area, thereby achieving the purpose of increasing oil and gas production and oil recovery rate. When performing staged fracturing, a temporary plugging tool needs to be used for isolation between layers to ensure that the pressure in the construction string does not leak. After the fracturing operation is completed, these tools need to be retrieved to facilitate the smooth progress of subsequent operations. Traditional plugging tools are usually made of steel, cast iron, composite materials, etc. After the fracturing construction is completed, these tools need to be removed by drilling and milling methods, which increases the operation cycle and cost, and is also prone to problems such as sticking and grinding of the drill and blockage of the hole. Magnesium alloy is an ideal material for manufacturing temporary plugging tools between layers of staged fracturing due to its advantages such as low density, high specific strength, low standard electrode potential, and good casting and processing performance.

[0003] At present, relevant technical research on magnesium alloy temporary plugging tools has been carried out both at home and abroad. However, due to China's vast territory, wide distribution of oil wells, large differences in downhole environments, water temperature varying in the range of 50 - 120°C and chloride ion concentration varying in the range of 3000 - 30000 ppm, different requirements are imposed on temporary plugging tools. The soluble bridge plugs studied at home and abroad at present have not been completely dissolved 15 days after actual downhole fracturing construction, and cannot well match the downhole environments in China. Therefore, in order to meet the application requirements of temporary plugging tools for fracturing exploitation, the dissolution performance and mechanical properties of soluble magnesium alloys still need to be improved. Summary of the Invention

[0004] In view of the above situation, the present invention aims to provide a low-cost and high-strength soluble magnesium alloy and a preparation method thereof, which are used to solve the problems of low strength and poor solubility of existing magnesium alloys used as temporary plugging tools.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] The present invention provides a low-cost and high-strength soluble magnesium alloy. The components of the low-cost and high-strength soluble magnesium alloy include, by mass percentage: Al: 7% - 9%, Ca: 0 - 1%, In: 0 - 0.5%, Cu: 0.1% - 1%, Ni: 0.1% - 1%, X: 0 - 1%, where X is one or more of FeCl3, C, and Zr, and the balance is Mg and unavoidable impurities.

[0007] Furthermore, the components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% to 9%, Ca: 0.2% to 0.9%, Cu: 0.1% to 0.95%, Ni: 0.15% to 0.85%.

[0008] Furthermore, the components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% to 9%, Ca: 0.2% to 0.9%, Cu: 0.1% to 0.95%, Ni: 0.15% to 0.85%, In: 0.1% to 0.5%.

[0009] Furthermore, the components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% to 9%, Ca: 0.2% to 0.9%, Cu: 0.1% to 0.95%, Ni: 0.15% to 0.85%, X: 0.1% to 1%.

[0010] Furthermore, the components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% to 9%, Ca: 0.2% to 0.9%, Cu: 0.1% to 0.95%, Ni: 0.15% to 0.85%, In: 0.1% to 0.5%, X: 0.1% to 1%.

[0011] Furthermore, the microstructure of the low-cost high-strength soluble magnesium alloy includes an α-Mg matrix, and Mg 17 Al 12 , MgAlCu and MgAlNi precipitation phases.

[0012] The present invention also provides a preparation method of the above-mentioned low-cost high-strength soluble magnesium alloy, including the following steps:

[0013] Step 1, raw material treatment: Weigh the required raw materials according to the mass percentage, and pre-treat the raw materials;

[0014] Step 2, melting: Heat the crucible to 680 - 780 °C. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium is melted, add the remaining raw materials in sequence. After all are melted, stir and then let it stand to obtain a magnesium alloy melt;

[0015] Step 3, casting: Introduce the magnesium alloy melt into the mold at 680 °C - 740 °C for continuous casting;

[0016] Step 4, two-stage homogenization treatment;

[0017] Step 5, hot extrude the homogenized billet;

[0018] Step 6, perform solution aging treatment on the extruded soluble magnesium alloy bar.

[0019] Further, in step 2, the heating rate is 15-25 °C / min.

[0020] Further, in step 4, the steps of the double-stage homogenization treatment include:

[0021] S401. Keep the temperature at 280-350 °C for 3-5 h;

[0022] S402. Continue to raise the temperature to 380-420 °C and keep the temperature for 15-30 h.

[0023] Further, in step 5, the extrusion speed during hot extrusion is 0.1-2 m / min, the extrusion temperature is 250-400 °C, and the extrusion ratio is 16-28:1.

[0024] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0025] a) The low-cost high-strength soluble magnesium alloy of the present invention introduces high-potential copper and nickel elements, and precipitates high-potential precipitation phases such as Mg2Cu, Mg2Ni, MgAlCu, and MgAlNi in the magnesium alloy, thereby significantly increasing the dissolution rate of the magnesium alloy; and a large amount of Mg 17 Al 12 phase can be precipitated, which can not only improve the mechanical properties of the soluble magnesium alloy, but also change the dissolution rate of the alloy; ensuring that the low-cost high-strength soluble magnesium alloy of the present invention has high strength and high dissolution rate.

[0026] b) The low-cost high-strength soluble magnesium alloy of the present invention adds a part of Ca element. On the one hand, it improves the thermal stability of the Mg 17 Al 12 phase and improves the high-temperature mechanical properties of the soluble magnesium alloy. On the other hand, the Ca element is easily solid-solved in the Mg 17 Al 12 phase, which can increase the potential difference between the matrix and the Mg 17 Al 12 phase, thereby increasing the dissolution rate of the magnesium alloy.

[0027] c) The low-cost high-strength soluble magnesium alloy of the present invention adds a small amount of In element, which has an activating effect on the corrosion of the magnesium alloy and can destroy the surface oxide film formed during the corrosion of the magnesium alloy, thereby increasing the dissolution rate of the magnesium alloy.

[0028] d) The low-cost high-strength soluble magnesium alloy of the present invention can add FeCl3 powder as a grain refiner during melting, which can not only improve the mechanical properties of the magnesium alloy by refining grains, but also add high-potential Fe element to the magnesium alloy matrix to increase the dissolution rate of the magnesium alloy.

[0029] e) In the preparation method of the low-cost and high-strength soluble magnesium alloy of the present invention, through the process steps and parameter control of melting, casting, double-stage homogenization treatment, extrusion, and solution aging treatment, the quantity, size, morphology, and distribution characteristics of these high-potential precipitation phases can be controlled, thereby controlling the dissolution rate of the soluble magnesium alloy.

[0030] f) In the preparation method of the low-cost and high-strength soluble magnesium alloy of the present invention, in order to ensure the uniform distribution of high-melting-point elements such as Ni and Cu in the melt, electromagnetic stirring is added at the crystallizer position, reducing the segregation of Ni and Cu in the continuous casting billet of the soluble magnesium alloy, thereby reducing the performance fluctuation of the soluble magnesium alloy.

[0031] g) The tensile strength of the low-cost and high-strength soluble magnesium alloy of the present invention is above 350 MPa (355 - 430 MPa), the yield strength is above 220 MPa (228 - 330 MPa), the elongation is above 5%, for example (5.4 - 9%), and the corrosion rate in a 3% KCl solution at 93 °C is 30 mg / cm 2 *h or above, for example (32 - 120 mg / cm 2 *h).

[0032] h) The low-cost and high-strength soluble magnesium alloy of the present invention has high strength, fast dissolution rate, simple preparation method, low content of added metal elements such as Ni and Cu, low preparation cost, and can adapt to different downhole working environments required for fracturing and production temporary plugging tools through the combination of composition design and process control of the preparation method. It is suitable for processing and preparing temporary plugging tools used in the fracturing process of shale gas exploitation, such as soluble bridge plugs, soluble fracturing balls, etc.

[0033] Other features and advantages of the present invention will be described in the following specification, and some of them will become obvious from the specification or be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the content specifically pointed out in the written specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings are only for the purpose of showing specific embodiments and are not considered as limitations to the present invention. Throughout the drawings, the same reference signs represent the same components.

[0035] Figure 1 It is the microstructure diagram of the soluble magnesium alloy of Example 1;

[0036] Figure 2 It is the microstructure diagram of the soluble magnesium alloy of Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings, wherein the drawings form a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention.

[0038] The present invention provides a low-cost, high-strength soluble magnesium alloy. The components of the above low-cost, high-strength soluble magnesium alloy include, by mass percentage: Al: 7% - 9%, Ca: 0 - 1%, In: 0 - 0.5%, Cu: 0.1% - 1%, Ni: 0.1% - 1%, X: 0 - 1%, where X is one or more of FeCl3, C, and Zr, and the balance is Mg and inevitable impurities.

[0039] The functions and dosage selections of the components contained in the present invention are specifically described as follows:

[0040] Al: The Al element is the main strengthening element in the soluble magnesium alloy of the present invention. The saturation solubility of Al in Mg is 12.7%, and the solubility of Al in Mg at room temperature is 2%. Therefore, Al can have the effects of solid solution strengthening and age hardening on Mg. Al solid solution in the Mg matrix can improve the strength and ductility of the magnesium alloy. When aging, the precipitation of β-Mg 17 Al 12 phase can significantly improve the yield strength and tensile strength of the alloy. When the Al content exceeds 8%, the β-Mg 17 Al 12 phase precipitates along the grain boundaries in a discontinuous network form, significantly damaging the plastic deformation ability of the alloy. With the increase of the Al element content, the precipitation of β-Mg 17 Al 12 phase between the grain boundaries increases. Considering that some Al elements in the soluble magnesium alloy of the present invention can form precipitation phases with Cu and Ni during solidification, the Al element content in the alloy can be appropriately increased. Therefore, taking all factors into consideration, the Al element content in the present invention is controlled at 7% - 9%.

[0041] Ca: It not only has good flame retardant properties, can inhibit the burning loss during the melting and casting of magnesium alloys, improve the quality of magnesium alloy castings, but also can refine grains, thereby improving the strength and toughness of the alloy and improving the creep resistance at high temperatures. When the Ca element content is greater than 1%, it is easy to form a network-like Al2Ca phase distributed along the grain boundaries, resulting in a decrease in the ultimate tensile strength and elongation. Therefore, taking all factors into consideration, the Ca element content in the present invention is controlled at 0 - 1%.

[0042] Cu, Ni: Both Cu and Ni are high-potential elements. In the magnesium alloy, high-potential precipitation phases such as Mg2Cu, Mg2Ni, MgAlCu, and MgAlNi precipitate, which can significantly increase the dissolution rate of the magnesium alloy. Moreover, as the contents of Ni and Cu increase, the dissolution rate of the magnesium alloy gradually rises. However, due to the excessive addition of Ni and Cu elements, it will cause the formation of coarse secondary phases in the magnesium alloy, affecting the plastic deformation ability of the magnesium alloy. Therefore, considering comprehensively, the contents of Ni and Cu in this invention are both controlled within 0.1% - 1%.

[0043] In: The In element can reduce the solubility of the Al element in the Mg matrix and refine the precipitated Mg 17 Al 12 phase. At the same time, it can also destroy the surface oxide film of the Al-containing magnesium alloy, all of which accelerate the dissolution of the magnesium alloy. However, due to the relatively high price of In, considering the cost factor of the alloy, the content of In in this invention is controlled within 0 - 0.5%.

[0044] X: X is one or more of elements such as FeCl3, C, and Zr. Its main function is to provide heterogeneous nucleation during solidification to refine the grain size of the magnesium alloy, thereby improving the mechanical properties of the magnesium alloy. However, since refining the grains will reduce the dissolution rate of the magnesium alloy, the content of X in this invention is controlled within 0 - 1%. In addition, since FeCl3 can provide a small amount of high-potential Fe elements while refining the grains, it can promote the dissolution of the magnesium alloy while improving the mechanical properties. Therefore, FeCl3 is preferably used as the grain refiner during the production process.

[0045] To further improve the comprehensive properties of the above-mentioned low-cost high-strength soluble magnesium alloy, the components of the above-mentioned low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%.

[0046] To further improve the comprehensive properties of the above-mentioned low-cost high-strength soluble magnesium alloy, the components of the above-mentioned low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%, In: 0.1% - 0.5%.

[0047] To further improve the comprehensive properties of the above-mentioned low-cost high-strength soluble magnesium alloy, the components of the above-mentioned low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%, X: 0.1% - 1%.

[0048] In order to further improve the comprehensive properties of the above-mentioned low-cost and high-strength soluble magnesium alloy, the components of the above-mentioned low-cost and high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% to 9%, Ca: 0.2% to 0.9%, Cu: 0.1% to 0.95%, Ni: 0.15% to 0.85%, In: 0.1% to 0.5%, X: 0.1% to 1%.

[0049] Specifically, the microstructure of the soluble magnesium alloy of the present invention includes an α-Mg matrix, and Mg 17 Al 12 , MgAlCu and MgAlNi.

[0050] Specifically, the microstructure of the soluble magnesium alloy of the present invention includes an α-Mg matrix, and Mg 17 Al 12 , MgAlCu, MgAlNi and Fe.

[0051] Specifically, the microstructure of the soluble magnesium alloy of the present invention includes an α-Mg matrix, and Mg 17 Al 12 , MgAlCu, MgAlNi and Al4C3.

[0052] Specifically, the grain size of the soluble magnesium alloy of the present invention is 10 to 50 μm, such as 14 to 32 μm.

[0053] On the other hand, the present invention also provides a method for preparing a low-cost and high-strength soluble magnesium alloy, including the following steps:

[0054] Step 1, raw material treatment: Weigh the required raw materials according to the mass percentage and pre-treat the raw materials;

[0055] Step 2, melting: Heat the crucible to 680 to 780 °C, first put pure magnesium into the crucible, use a mixed gas of SF6 and CO2 to protect the melt during the melting process. After all the pure magnesium is melted, add the remaining raw materials in sequence (such as intermediate alloys like AlCu, MgNi, alloy ingots like pure Al, pure Ca, and FeCl3 powder or C). After all are melted, stir and then let it stand to obtain a magnesium alloy melt;

[0056] Step 3, casting: Introduce the magnesium alloy melt into the mold at 680 °C to 740 °C for continuous casting;

[0057] Step 4, two-stage homogenization treatment;

[0058] Step 5, hot extrude the homogenized billet;

[0059] Step 6, perform solution aging treatment on the extruded soluble magnesium alloy bar.

[0060] Specifically, in the above step 1, the pretreatment includes polishing off the oxide layer on the surface of the raw material with sandpaper, and then drying the raw material in a drying oven to remove the moisture on the surface of the raw material.

[0061] Specifically, in the above step 2, the heating rate is 15 - 25 °C / min.

[0062] Specifically, in the above step 2, in order to ensure the uniformity of the alloy composition, after complete melting, stir for 5 - 10 min, and then let it stand for 10 - 20 min.

[0063] Specifically, in the above step 3, the drawing speed is 10 - 70 mm / min. In order to ensure the uniform distribution of high melting point elements such as Ni and Cu in the melt, when the content of Ni and Cu elements > 0.7%, electromagnetic stirring is added at the mold position, so that the segregation of Ni and Cu in the continuously cast billet of soluble magnesium alloy is reduced, thereby reducing the performance fluctuation of the soluble magnesium alloy.

[0064] Specifically, in the above step 4, in order to eliminate the eutectic α-Mg phase, Mg 17 Al 12 phase and the divorced eutectic Mg 17 Al 12 phase, a two-stage homogenization treatment is carried out. The steps of the two-stage homogenization treatment include:

[0065] S401. Keep it at 280 - 350 °C for 3 - 5 h;

[0066] S402. Continue to heat up to 380 - 420 °C and keep it for 15 - 30 h.

[0067] Specifically, in the above step 5, molybdenum disulfide is used for lubrication during the extrusion process.

[0068] Specifically, in the above step 5, the extrusion speed during hot extrusion is 0.1 - 2 m / min, the extrusion temperature is 250 - 400 °C, and the extrusion ratio is (16 - 28):1.

[0069] Specifically, in the above step 6, the solution treatment process parameters are (380 - 420 °C) × (3 - 10) h, and the aging process is (140 °C - 280 °C) × (3 - 100) h.

[0070] Specifically, in the above step 6, the inventor found through in-depth research that: aging at 180 °C, the peak aging temperature is 20 h, at this time the strength and plasticity match well, but the corrosion rate is relatively low; while aging at 220 °C, the peak aging temperature is 22 h, at this time the strength and corrosion rate are relatively high, but the elongation rate is relatively low. Therefore, in the actual production process, the process parameters can be selected according to the emphasis on performance requirements.

[0071] Specifically, in the microstructure of the soluble magnesium alloy of the present invention, the contents of MgAlCu and MgAlNi are in the range of 1% to 10%, and increase with the increase of the contents of Ni and Cu. Mg 17 Al 12 The type, morphology, volume fraction of the phase are related to the aging temperature and time. When aging at temperatures above 200 °C, the continuously precipitated (CP) Mg 17 Al 12 phase has a volume fraction in the range of 10% to 50%, and the discontinuously precipitated (DP) Mg 17 Al 12 phase has a volume fraction in the range of 5% to 40%. With the increase of temperature, the CP-Mg 17 Al 12 phase in the alloy increases, and the DP-Mg 17 Al 12 phase decreases; when aging at temperatures below 200 °C, the volume fraction of the DP-Mg 17 Al 12 phase is 5% to 50%, and the volume fraction of the CP-Mg 17 Al 12 phase is in the range of 0 to 15%. With the decrease of temperature, the CP-Mg 17 Al 12 phase gradually disappears, and the DP-Mg 17 Al 12 phase in the alloy increases but the precipitation rate gradually slows down. When aging at temperatures below 140 °C, the DP-Mg 17 Al 12 phase hardly precipitates either.

[0072] The low-cost high-strength soluble magnesium alloy of the present invention introduces high-potential copper and nickel elements, and precipitates high-potential precipitated phases such as Mg2Cu, Mg2Ni, MgAlCu, and MgAlNi in the magnesium alloy, thereby significantly improving the dissolution rate of the magnesium alloy; and a large amount of Mg 17 Al 12 phase can be precipitated, which can not only improve the mechanical properties of the soluble magnesium alloy, but also change the dissolution rate of the alloy; ensuring that the low-cost high-strength soluble magnesium alloy of the present invention has high strength and high dissolution rate.

[0073] The low-cost high-strength soluble magnesium alloy of the present invention adds a part of Ca element. On the one hand, it improves the thermal stability of the Mg 17 Al 12 phase and improves the high-temperature mechanical properties of the soluble magnesium alloy. On the other hand, the Ca element is easily solid-solved in the Mg 17 Al 12 phase, which can increase the potential difference between the matrix and the Mg 17 Al 12 phase, thereby improving the dissolution rate of the magnesium alloy.

[0074] The low-cost, high-strength soluble magnesium alloy of the present invention adds a small amount of In element, which has an activating effect on the corrosion of the magnesium alloy, can destroy the surface oxide film formed during the corrosion of the magnesium alloy, and thus improve the dissolution rate of the magnesium alloy.

[0075] During the melting of the low-cost, high-strength soluble magnesium alloy of the present invention, FeCl3 powder can be added as a grain refiner, which can not only improve the mechanical properties of the magnesium alloy by refining the grains, but also add high-potential Fe element to the magnesium alloy matrix to improve the dissolution rate of the magnesium alloy.

[0076] In the preparation method of the low-cost, high-strength soluble magnesium alloy of the present invention, through the process steps and parameter control of melting, casting, double-stage homogenization treatment, extrusion and solution aging treatment, the quantity, size, morphology and distribution characteristics of these high-potential precipitation phases can be controlled, so as to control the dissolution rate of the soluble magnesium alloy.

[0077] In the preparation method of the low-cost, high-strength soluble magnesium alloy of the present invention, in order to ensure the uniform distribution of high-melting-point elements such as Ni and Cu in the melt, electromagnetic stirring is added at the crystallizer position, so that the segregation of Ni and Cu in the continuous casting billet of the soluble magnesium alloy is reduced, thereby reducing the performance fluctuation of the soluble magnesium alloy.

[0078] The tensile strength of the low-cost, high-strength soluble magnesium alloy of the present invention is above 350 MPa (355 - 430 MPa), the yield strength is above 220 MPa (228 - 330 MPa), the elongation is above 5%, for example (5.4 - 9%), and the corrosion rate in 3% KCl solution at 93 °C is 30 mg / cm 2 *h or more, for example (32 - 120 mg / cm 2 *h).

[0079] The low-cost, high-strength soluble magnesium alloy of the present invention has high strength, fast dissolution rate, simple preparation method, low content of added metal elements such as Ni and Cu, low preparation cost, and can adapt to different downhole working environments required for fracturing and production temporary plugging tools through the combination of composition design and process control of the preparation method. It is suitable for processing and preparing temporary plugging tools used in the fracturing process of shale gas exploitation, such as soluble bridge plugs, soluble fracturing balls, etc.

[0080] Examples 1 - 8

[0081] The following takes specific examples and comparative examples to demonstrate the advantages of precise control of the composition and process parameters of the low-cost, high-strength soluble magnesium alloy of the present invention.

[0082] Examples 1 - 8 of the present invention provide a low-cost, high-strength soluble magnesium alloy and its preparation method. The chemical compositions of the steels in Examples 1 - 8 are shown in Table 1.

[0083] The preparation method of Example 1 is as follows:

[0084] (1) Raw material treatment: Weigh the required raw materials according to the weight percentage, polish off the oxide layer on the metal surface with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the surface of the raw materials;

[0085] (2) Melting: Heat the crucible to 720 °C at a heating rate of 20 °C / min. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium has melted, successively add intermediate alloys such as AlCu and MgNi, alloy ingots such as pure Al and pure Ca. After all have melted, stir for 5 min to ensure the uniformity of the alloy composition, and then let it stand for 20 min;

[0086] (3) Casting: Introduce the magnesium alloy melt into the mold at 700 °C for continuous casting, and the drawing speed is 50 mm / min;

[0087] (4) Homogenization treatment: Perform a two-stage homogenization treatment, and the homogenization conditions are 330 °C × 5 h + 400 °C × 20 h;

[0088] (5) Hot extrusion: Perform hot extrusion on the cast billet after homogenization treatment. The extrusion speed during hot extrusion is 0.5 m / min, the extrusion temperature is 300 °C, the extrusion ratio is 22.5:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0089] (6) Heat treatment: Perform solution aging treatment on the extruded soluble magnesium alloy rod. The solution process is 400 °C × 5 h, and the aging process is 220 °C × 20 h.

[0090] The preparation method of Example 2 is as follows:

[0091] (1) Raw material treatment: Weigh the required raw materials according to the weight percentage, polish off the oxide layer on the metal surface with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the surface of the raw materials;

[0092] (2) Melting: Heat the crucible to 760 °C at a heating rate of 20 °C / min. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium has melted, successively add intermediate alloys such as AlCu and MgNi, alloy ingots such as pure Al and pure Ca. After all have melted, stir for 5 min to ensure the uniformity of the alloy composition, and then let it stand for 20 min;

[0093] (3) Casting: Introduce the magnesium alloy melt into the mold at 750 °C for continuous casting, and the drawing speed is 20 mm / min. To ensure the uniform distribution of Ni and Cu elements in the casting and reduce their segregation, an electromagnetic stirring with a magnetic field strength of 50 Gs is added at the mold position;

[0094] (4) Homogenization treatment: Perform a two-stage homogenization treatment, and the homogenization conditions are 330 °C × 5 h + 400 °C × 30 h;

[0095] (5) Hot extrusion: Perform hot extrusion on the billet after homogenization treatment. The extrusion speed during hot extrusion is 0.2 m / min, the extrusion temperature is 400 °C, the extrusion ratio is 18.5:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0096] (6) Heat treatment: Perform solution aging treatment on the extruded soluble magnesium alloy rod. The solution process is 400 °C × 5 h, and the aging process is 180 °C × 20 h.

[0097] The preparation method of Example 3 is as follows:

[0098] (1) Raw material treatment: Weigh the required raw materials according to the weight percentage, polish off the metal surface oxide layer with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the surface of the raw materials;

[0099] (2) Melting: Heat the crucible to 740 °C at a heating rate of 20 °C / min. First, put pure magnesium into the crucible. Use a mixed gas of SF6 and CO2 to protect the melt during the melting process. After all the pure magnesium is melted, successively add intermediate alloys such as AlCu and MgNi, pure Al, pure Ca, pure In and other alloy ingots. After all are melted, stir for 5 min to ensure the uniformity of the alloy composition, and then let it stand for 20 min;

[0100] (3) Casting: Introduce the magnesium alloy melt into the mold at 720 °C for continuous casting, and the drawing speed is 30 mm / min;

[0101] (4) Homogenization treatment: Perform a two-stage homogenization treatment, and the homogenization conditions are 320 °C × 5 h + 410 °C × 25 h;

[0102] (5) Hot extrusion: Perform hot extrusion on the billet after homogenization treatment. The extrusion speed during hot extrusion is 0.5 m / min, the extrusion temperature is 360 °C, the extrusion ratio is 20:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0103] (6) Heat treatment: Perform solution aging treatment on the extruded soluble magnesium alloy rod. The solution process is 400 × 5 h, and the aging process is 200 × 30 h

[0104] The preparation method of Example 4 is as follows:

[0105] (1) Raw material treatment: Weigh the required raw materials according to the weight percentage, polish off the metal surface oxide layer with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the surface of the raw materials;

[0106] (2) Melting: Heat the crucible to 740 °C at a heating rate of 20 °C / min. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium has melted, successively add intermediate alloys such as AlCu and MgNi, pure Al, pure Ca, pure In and other alloy ingots. After all have melted, stir for 5 min to ensure uniform alloy composition, and then let it stand for 20 min;

[0107] (3) Casting: Introduce the magnesium alloy melt into the mold at 720 °C for continuous casting, and the drawing speed is 30 mm / min;

[0108] (4) Homogenization treatment: Conduct a two-stage homogenization treatment, and the homogenization conditions are 320 °C × 5 h + 410 °C × 30 h;

[0109] (5) Hot extrusion: Perform hot extrusion on the homogenized billet. The extrusion speed during hot extrusion is 0.5 m / min, the extrusion temperature is 380 °C, the extrusion ratio is 22:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0110] (6) Heat treatment: Conduct solution aging treatment on the extruded soluble magnesium alloy rod. The solution process is 400 °C × 5 h, and the aging process is 180 °C × 50 h.

[0111] The preparation method of Example 5 is as follows:

[0112] (1) Raw material treatment: Weigh the required raw materials by weight percentage, polish off the metal surface oxide layer with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the raw material surface;

[0113] (2) Melting: Heat the crucible to 720 °C at a heating rate of 20 °C / min. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium has melted, successively add intermediate alloys such as AlCu and MgNi, pure Al, pure Ca and other alloy ingots. After all have melted, stir for 5 min to ensure uniform alloy composition. After standing for 10 min, slowly press the preheated FeCl3 powder into the alloy liquid at 1 / 2 - 1 / 3 depth with a preheated bell jar, stir for 5 min and then let it stand for 10 min;

[0114] (3) Casting: Introduce the magnesium alloy melt into the mold at 700 °C for continuous casting, and the drawing speed is 50 mm / min;

[0115] (4) Homogenization treatment: Conduct a two-stage homogenization treatment, and the homogenization conditions are 330 °C × 5 h + 400 °C × 25 h;

[0116] (5) Hot extrusion: The homogenized billet is subjected to hot extrusion. The extrusion speed during hot extrusion is 0.5 m / min, the extrusion temperature is 320 °C, the extrusion ratio is 26:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0117] (6) Heat treatment: The extruded soluble magnesium alloy bar stock is subjected to solution aging treatment. The solution process is 400 °C × 5 h, and the aging process is 260 °C × 50 h.

[0118] The preparation method of Example 6 is as follows:

[0119] (1) Raw material treatment: Weigh the required raw materials according to the weight percentage, polish off the metal surface oxide layer with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the surface of the raw materials;

[0120] (2) Melting: Heat the crucible to 750 °C at a heating rate of 20 °C / min. First, put pure magnesium into the crucible. During the melting process, a mixed gas of SF6 and CO2 is used to protect the melt. After all the pure magnesium has melted, add intermediate alloys such as AlCu and MgNi, pure Al, pure Ca alloy ingots in sequence. After all have melted, stir for 5 min to ensure the uniformity of the alloy composition. After standing for 10 min, slowly press the preheated FeCl3 powder into the alloy liquid at 1 / 2 - 1 / 3 depth with a preheated bell jar, stir for 5 min and then stand for 10 min;

[0121] (3) Casting: Introduce the magnesium alloy melt into the mold at 740 °C for continuous casting, and the drawing speed is 30 mm / min;

[0122] (4) Homogenization treatment: Perform double-stage homogenization treatment, and the homogenization conditions are 330 °C × 5 h + 400 °C × 30 h;

[0123] (5) Hot extrusion: The homogenized billet is subjected to hot extrusion. The extrusion speed during hot extrusion is 0.5 m / min, the extrusion temperature is 360 °C, the extrusion ratio is 22:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0124] (6) Heat treatment: The extruded soluble magnesium alloy bar stock is subjected to solution aging treatment. The solution process is 400 °C × 3 h, and the aging process is 180 °C × 70 h.

[0125] The preparation method of Example 7 is as follows:

[0126] (1) Raw material treatment: Weigh the required raw materials according to the weight percentage, polish off the metal surface oxide layer with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the surface of the raw materials;

[0127] (2) Melting: Heat the crucible to 720°C at a heating rate of 20°C / min. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium has melted, successively add intermediate alloys such as AlCu and MgNi, alloy ingots such as pure Al and pure Ca. After all have melted, stir for 5 min to ensure uniform alloy composition. After standing for 10 min, add 0.5% C element in the form of Al-C intermediate alloy, stir for 5 min and then stand for 10 min;

[0128] (3) Casting: Introduce the magnesium alloy melt into the mold at 700°C for continuous casting, and the drawing speed is 40 mm / min;

[0129] (4) Homogenization treatment: Conduct a two-stage homogenization treatment, and the homogenization conditions are 330°C × 5 h + 400°C × 20 h

[0130] (5) Hot extrusion: Perform hot extrusion on the homogenized billet. The extrusion speed during hot extrusion is 0.3 m / min, the extrusion temperature is 300°C, the extrusion ratio is 28:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0131] (6) Heat treatment: Conduct solution aging treatment on the extruded soluble magnesium alloy rod. The solution process is 400°C × 5 h, and the aging process is 220°C × 50 h.

[0132] The preparation method of Example 8 is as follows:

[0133] (1) Raw material treatment: Weigh the required raw materials by weight percentage, polish off the metal surface oxide layer with sandpaper, and then put the metal raw materials into a drying oven to dry to remove the moisture on the raw material surface;

[0134] (2) Melting: Heat the crucible to 740°C at a heating rate of 20°C / min. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium has melted, successively add intermediate alloys such as AlCu and MgNi, alloy ingots such as pure Al and pure Ca. After all have melted, stir for 5 min to ensure uniform alloy composition. After standing for 10 min, after all have melted, stir for 5 min to ensure uniform alloy composition. After standing for 10 min, add C element in the form of Al-C intermediate alloy, stir for 5 min and then stand for 10 min;

[0135] (3) Casting: Introduce the magnesium alloy melt into the mold at 720°C for continuous casting, and the drawing speed is 30 mm / min;

[0136] (4) Homogenization treatment: Conduct a two-stage homogenization treatment, and the homogenization conditions are 330°C × 5 h + 400°C × 30 h;

[0137] (5) Hot extrusion: The homogenized billet is subjected to hot extrusion. The extrusion speed during hot extrusion is 0.5 m / min, the extrusion temperature is 350 °C, the extrusion ratio is 26:1, and molybdenum disulfide is used for lubrication during the extrusion process;

[0138] (6) Heat treatment: The extruded soluble magnesium alloy rod is subjected to solution aging treatment. The solution process is 400 °C × 3 h, and the aging process is 200 °C × 50 h.

[0139] During the research process, the inventors conducted a large number of experimental studies, and some solutions with poor performance are used as comparative examples.

[0140] Comparative Example 1

[0141] This comparative example provides a soluble magnesium alloy, the components of which are shown in Table 1 above. The preparation method is the same as that of Example 1 and will not be elaborated here.

[0142] Comparative Example 2

[0143] This comparative example provides a soluble magnesium alloy, the components of which are shown in Table 1 above. The preparation method is the same as that of Example 1 and will not be elaborated here. In this comparative example, due to the low Al content, the number of Mg 17 Al 12 phase decreases and the mechanical properties decrease.

[0144] Comparative Example 3

[0145] This comparative example provides a soluble magnesium alloy, the components of which are shown in Table 1 above. The preparation method is the same as that of Example 5 and will not be elaborated here.

[0146] In this comparative example, an excessive amount of Fe is added. It is insoluble in the Mg matrix and forms coarse Fe single substances at the grain boundaries, seriously affecting the plasticity of the alloy.

[0147] Comparative Example 4

[0148] The composition of this example is the same as that of Example 1, the components of which are shown in Table 1 above. The preparation method is roughly the same as that of Case 1, except that the extrusion temperature is 410 °C, the extrusion speed is 0.3 m / min, the solution process is 420 °C × 5 h, and the aging process is 120 °C × 50 h.

[0149] In this comparative example, due to the too low aging temperature, the precipitation of the strengthening phase Mg 17 Al 12 phase is less, so the mechanical properties decrease.

[0150] The metallographic structures and main performance test results of the examples and comparative examples are shown in Table 2.

[0151] Table 1 Chemical composition, wt%

[0152] Mg Al Ca Cu Ni In X Example 1 Bal. 7.52 0.25 0.19 0.21 0 0 Example 2 Bal. 8.94 0.72 0.91 0.78 0 0 Example 3 Bal. 8.35 0.23 0.20 0.19 0.15 0 Example 4 Bal. 7.41 0.31 0.23 0.24 0.47 0 Example 5 Bal. 8.52 0.29 0.26 0.28 0.23 <![CDATA[0.21(FeCl3)]]> Example 6 Bal. 7.84 0.43 0.64 0.41 0.31 <![CDATA[0.79(FeCl3)]]> Example 7 Bal. 8.56 0.24 0.24 0.25 0 0.52(C) Example 8 Bal. 8.01 0.55 0.43 0.38 0 0.92(C) Comparative Example 1 Bal. 8.34 0.52 0 0 0 0 Comparative Example 2 Bal. 5.22 0.26 0.41 0.54 0 0 Comparative Example 3 Bal. 8.34 1.68 0.22 0.20 0 <![CDATA[1.31(FeCl3)]]> Comparative Example 4 Bal. 7.52 0.25 0.19 0.21 0 0

[0153] Table 2 Detection Results of Tissues and Partial Properties

[0154]

[0155]

[0156] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-cost and high-strength soluble magnesium alloy, characterized in that, The components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7% - 9%, Ca: 0.2% - 0.9%, In: 0 - 0.5%, Cu: 0.1% - 1%, Ni: 0.1% - 1%, X: 0 - 1%, where X is one or more of FeCl3, C, and Zr, and the balance is Mg and unavoidable impurities; The microstructure of the low-cost high-strength soluble magnesium alloy includes an α-Mg matrix and Mg 17 Al 12 , MgAlCu and MgAlNi precipitation phases, and the grain size is 14-50 μm; The tensile strength of the low-cost and high-strength soluble magnesium alloy is above 350 MPa, the yield strength is above 220 MPa, the elongation is above 5%, and the corrosion rate in a 3% KCl solution at 93 °C is 30 mg / cm 2 *h or more.

2. The low-cost and high-strength soluble magnesium alloy according to claim 1, wherein The components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%.

3. The low-cost high-strength soluble magnesium alloy according to claim 1, wherein The components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%, In: 0.1% - 0.5%.

4. The low-cost high-strength soluble magnesium alloy according to claim 1, wherein The components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%, X: 0.1% - 1%.

5. The low-cost high-strength soluble magnesium alloy according to claim 1, wherein The components of the low-cost high-strength soluble magnesium alloy include, by mass percentage: Al: 7.3% - 9%, Ca: 0.2% - 0.9%, Cu: 0.1% - 0.95%, Ni: 0.15% - 0.85%, In: 0.1% - 0.5%, X: 0.1% - 1%.

6. A method for preparing a low-cost high-strength soluble magnesium alloy according to any one of claims 1 to 5, characterized in that, It includes the following steps: Step 1, raw material treatment: Weigh the required raw materials according to the mass percentage and pre-treat the raw materials; Step 2, melting: Heat the crucible to 680 - 780 °C. First, put pure magnesium into the crucible. During the melting process, use a mixed gas of SF6 and CO2 to protect the melt. After all the pure magnesium is melted, add the remaining raw materials in sequence. After all are melted, stir and then let it stand to obtain a magnesium alloy melt; Step 3, casting: Introduce the magnesium alloy melt into the mold at 680 °C - 740 °C for continuous casting; Step 4, two-stage homogenization treatment; Step 5, hot extrude the cast billet after homogenization treatment; Step 6, perform solution aging treatment on the extruded soluble magnesium alloy rod.

7. The preparation method according to claim 6, characterized in that, In step 2, the heating rate is 15 - 25 °C / min.

8. The preparation method according to claim 6, characterized in that, In step 4, the steps of two-stage homogenization treatment include: S401, keep it at 280 - 350 °C for 3 - 5 h; S402, continue to heat up to 380 - 420 °C and keep it for 15 - 30 h.

9. The preparation method according to any one of claims 6 to 8, characterized in that, In step 5, the extrusion speed during hot extrusion is 0.1 - 2 m / min, the extrusion temperature is 250 - 400 °C, and the extrusion ratio is 16 - 28:1.

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